Garrison, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38 °F (low) to 58.3 °F (high). Annual precipitation averages 37.6 Inches. Garrison is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 10.6 °F | 27.4 °F | 1.14 in. |
| February | 14.4 °F | 32.1 °F | 1.25 in. |
| March | 25.8 °F | 45.3 °F | 2.09 in. |
| April | 36.9 °F | 59.9 °F | 3.82 in. |
| May | 49.2 °F | 71.1 °F | 4.84 in. |
| June | 59.8 °F | 80.5 °F | 5.54 in. |
| July | 63.0 °F | 83.8 °F | 4.36 in. |
| August | 60.2 °F | 81.9 °F | 4.29 in. |
| September | 51.5 °F | 75.7 °F | 3.69 in. |
| October | 39.6 °F | 62.5 °F | 2.92 in. |
| November | 27.5 °F | 46.4 °F | 2.11 in. |
| December | 17.0 °F | 33.1 °F | 1.57 in. |
| Annual | 38 °F | 58.3 °F | 37.62 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |